The present invention relates to an ultrasonic type blood flow amount measuring apparatus for non-invasively measuring the amount of blood flow through a region of interest of a subject to be diagnosed, through the utilization of an ultrasonic Doppler effect.
In conventional techniques, the ultrasonic Doppler method has been utilized to evaluate the amount of blood flow and the apparatus according to the method is commercially available. The blood flow amount, in such an apparatus, is calculated by employing the ultrasonic Doppler method as follows. Continuous ultrasonic beams from two ultrasonic transducers are emitted to cross at a sampling point of a blood vessel through two different paths. Two ultrasonic Doppler signals derived from receiving echoes are used to determine a blood flow direction and a steering line direction, and thus a velocity of blood flow along the direction of the blood vessel is calculated. A pulsed ultrasonic beam is emitted for calculating the sectional area of the blood vessel determined by the diameter of the blood vessel. Finally, the calculated sectional area and the calculated blood flow velocity are used to calculate the amount of blood flow.
In this case, since the two ultrasonic transducers are required to intersect their ultrasonic beams with each other, a probe containing the two transducers becomes bigger and more complicated in construction. Also an amount of blood flow in the heart of a patient cannot be measured.
A cardiac blood flow or a cardiac output (the amount of the cardiac blood flow per minute), which is delivered from the heart to the whole body, is a particularly important value as body information on diagnosis. However, it is practically difficult to measure the amount of blood flow of an aorta by the conventional method because ultrasonic beams emitted are limited into a certain range and an angle by the existence of the lungs and ribs. Moreover, the cardiac bloodstream, unlike blood vessels, does not have a uniform boundary of a sectional area nor can the direction of the blood flow be determined, therefore, it is even more difficult to measure the amount of blood flow by the conventional method. Extensive research has been conducted, but all the methods are complicated to operate and their precision is poor. Thus, they cannot be put to practical use.
Further, disclosed in U.S. Pat. No. 4,790,322 is an ultrasonic type blood flow amount measuring apparatus. This apparatus includes an ultrasonic transducer for steering a region of interest of a subject with an ultrasonic beam and receiving echoes from the region. There provided is a Doppler calculation section which detects a Doppler shift signal on a line orthogonal with the steering lines. Speeds of blood flows on the line are calculated from the Doppler shift signals, and thus an amount of blood flows passing through the region of interest can be evaluated from the speeds of blood flows and an area of section of the blood flow.
However, this blood flow amount measuring apparatus has a drawback in regard to precision in measurement. Since the measuring line is designated to be orthogonal with the steering lines, it is not guaranteed that the measuring line always properly covers the entire flow of blood. When the line is designated obliquely against the flow, the line sometimes fails to catch a blood flow at its end portions. This results in that a part of the blood flow bypasses the measuring line and leads to reduced precision of measurement.